The assignee of the present invention has, for a number of years, built lines of industrial pressure liquid filters including a compressed gas-powered vibrator unit within the filter housing. A number of patents have been issued to the present assignee in connection with filters of this type.
For example, U.S. Pat. No. 3,692,178, assigned to the assignee of the present invention, provides a compressed air powered vibrator suspended by elongate air input and output noses low in the filter housing, just below the bottom of the filter element, for agitating the processed liquid to be filtered within such housing.
A later U.S. Pat. No. 3,870,640, also assigned to the assignee of the present invention, shows development in which the vibrator is fixed to the bottom end of the filter element. The filter element depends from its top end, which is fixedly supported within the filter housing. In this instance, the vibrator actually vibrates the filter element to which it is attached and thereby is intended to inhibit the tendency of solids and the process liquid surrounding the filter element to cake on and block the filter element.
However, testing of the latter apparatus has shown that the vibrator tends to laterally vibrate the bottom end of the filter element to a substantially greater amplitude than the top end of the filter element, in a pendulum-like manner.
While satisfactory for most applications, if one were to use this filter unit in filtering liquids with extremely sticky solids content, such as modern automobile paints, the pendulum-like vibration characteristic of the filter element could risk a premature coating of the upper portion of the filter element. Further, care must be taken to mount the upper end of the filter element in a very robust manner to avoid mechanical fatigue to such mounting due to vibration over a period of use, in view of the support of the substantial weight of the vibrator dependently from the bottom of the filter element, if one needs to provide a relatively large vibration amplitude at the top of the filter element.
U.S. Pat. No. 4,836,922, also assigned to the assignee of the present invention, discloses a further development, namely a vibratorially self-cleaning filter unit particularly adapted to efficient filtering of liquids with sticky high solids content prone to clog the input side of the filter element. In particular, such filter has proven capable of efficient removal of unwanted solids from the high solids, sticky, viscous, high pigment finish coat paint now widely used in the automotive industry. In this patented filter unit, a filtered liquid outlet chamber is defined vertically between the cover of the filter housing and a plate spaced therebelow, from which plate depends the filter element or elements into the lower, inlet portion of the filter housing. The outlet chamber contains three evenly circumferentially spaced, vertical support rods that have tops welded to the bottom of the cover and bottoms welded to the top of the plate from which the filter elements depend. A vibrator comprises a housing closing a horizontal circular race, around which an inertia mass, for example a steel ball, is orbitable. The vibrator is fixed to the rods at a location between and spaced from each of the cover and plate. More particularly, the vibrator housing is shaped like a right circular cylinder snugly surrounded by and welded to the three support rods. An O-ring is disposed between the bottom of the plate and an upward facing step within the housing to enable the plate to carry out small amplitude horizontal vibration with respect to the housing. The orbiting inertia mass in the vibrator housing causes the vibrator housing to vibrate in a horizontal plane. The spacing of the vibrator below the fixed housing cover and the capability of the three support rods to flex with respect to the cover results in vibratory horizontal movement of the plate and relatively uniform horizontal vibratory motion of the filter elements along the vertical length thereof. In one successful embodiment, acceptable filter element vibration amplitude uniformity was obtained using relatively short filter elements, namely a trio of filter elements about 12 inches long with a diameter of 11/4 inch each. In one embodiment, satisfactory filtering and cleaning was obtained with a paint flow rate of 20-25 gallons per minute per square foot of filter element, through the filter unit. All in all, the performance of the patented apparatus as a filter for final coat paint of the mentioned type has been satisfactory.
A need exists, however, for an efficient self-cleaning filter for base coat of the type now used in the electrostatic dip coating of raw automotive vehicle bodies. This base coat has substantially different characteristics than the above-described finish coat. The E-coat has substantially less pigment than the finish coat paint, so there is less need to avoid pigment shear that might be caused by a vertical component of vibration of the filter elements. Particle size to be filtered out also differs, the lower limit being about 25 microns in the finish coat and about 50 microns in the base coat.
The base, or "E-coat" ("E" for electrostatically attracted) is a jelly-like material. It is high velocity sensitive and can thereby be stripped. Increasing flow restriction, either by raising velocity of flow or turning corners at high velocity tends to strip off parts of this gelatin-like material.
E-coat is also low velocity sensitive. Thus, once the filtered E-coat liquid leaves the filter element, applicant has found that the path out of the filter unit housing, from the filter element outlet to the housing outlet, should be kept as free as possible from obstructions, such as compressed gas supply and exhaust houses or vibrator support rods, and that the remaining obstructions in the flow path should be sized, shaped and located to minimize flow obstruction and dead zones, to provide a relatively smooth and open flow path from the filter element outlets to the housing outlet. Applicant has found that any pockets along the flow path should be shallow and shaped to provide some turbulence so that there is sufficient flow velocity therein as to prevent stagnation of filtered E-coat therein.
The gelatin-like consistency of the material is permitted due to the fact that it is not sprayed like a conventional paint, but rather is applied by dipping the vehicle bodies in a tank of the jelly-like material, wherein electrostatic means are provided to tightly and uniformly bond the gelatin-like E-coat to the vehicle bodies dipped in the tank.
It is particularly important that unwanted solids be filtered out of the E-coat in the tank because vehicle bodies remain immersed in the tank for a relatively long time, for example four hours, and failure to properly filter out impurities from the E-coat may not be discovered till after a vehicle body is removed from the tank, by which time several vehicle bodies may be blemished. Several vehicles are normally in the tank at one time, and tank size may run as high as 80,000 to 100,000 gallons. The E-coat and finish coat are relatively thin and thus small unwanted solids (hair, dirt particles, etc.) can noticeably blemish the final vehicle finish. This is not satisfactory and the E-coat must be efficiently filtered and thus maintained free of unwanted solids.
In view of the large size of the vehicle body dip bath, and the corresponding large volume of base coat liquid needed to fill it, the associated bank of filter units, sized to occupy a given space, must handle a higher flow rate during filtration than in the case of the final coat paint filter. At first glance, it would appear that the higher flow rates through a given filter unit could be obtained simply by upsizing the filter elements (increasing the diameter and length thereof) in the prior paint filter of the present assignee. However, applicant has determined that to do so would degrade the uniformity of vibration amplitude along the length of the filter elements and thereby degrade uniformity of vibratory cleaning of the filter elements along the lengths thereof. Further, applicant has determined that with the reduced pigment, and therefore with the reduced risk of pigmemt shear in the E-coat, by the outer surface of the vibrating paint filter element surface, cleaning efficiency could be enhanced by introduction of a modest amplitude .of vertical vibration of the filter element, i.e., vibratory movement lengthwise of the filter elements, so as to create something of a shear effect between the circumferential windings of the filter element and solids adhering thereto.
In one embodiment of the present invention, applicant has achieved substantial increase in filtering flow per filter unit by increasing filter tube diameter and length (for example 21/4" diameter.times.24" length vs. 11/4" tube diameter.times.12" length in the prior paint filter), thereby allowing a substantially higher liquid filtration rate (about 300 gallons per minute vs. about 30 gallons per minute in the prior paint filter, per filter unit). The vibrator is upsized by a small amount as to ball diameter and orbit diameter, but with very little increase in pressure air input, for example 7 cubic feet per minute (CFM) vs. 5 CFM in the prior paint filter. This achieves filter element vibration amplitude of sufficient uniformity along the length of the filter element, of horizontal vibrational amplitude and achieves a modest vertical vibratory amplitude (in one embodiment up to 0.030 inch horizontal vibratory amplitude and about 0.001 inch vertical vibratory amplitude at a frequency of 2000 to 4000 Hz).
Accordingly, the objects and purposes of the invention include provision of a vibrating filter which is made compact by housing the vibrator in the filtered liquid outlet chamber of the filter housing, in which the vibrator and its connection to the filter elements are sized and shaped and located in the housing outlet chamber to minimize interference with flow of filtered liquid from said filter elements through and out of the outlet chamber, in which the outlet chamber is free of energy supply cables or conduits to the vibrator, in which liquids including relatively gelatin-like liquids (particularly including electrostatic dip bath base coats for vehicles) can be efficiently filtered for long periods of time without need to disassemble the filter unit for cleaning, which the vibrator and filter elements connected thereto are together resiliently mounted with respect to the housing and removable as a single cartridge unit from the housing, in which vibration in a longitudinal as well as lateral direction is applied to the filter elements, and in which the filter unit is readily manufactured at reasonable cost and capable of a long service life with little or no maintenance.
The objects and purposes of this invention are met by providing a vibrating filter having a housing, top and bottom plates spaced vertically in an upper portion of the housing and defining an outlet chamber therebetween, at least one filter element dependent from the bottom plate into a filter chamber defined in the housing below the outlet chamber and a process liquid inlet into the filter chamber and a filtered liquid outlet from the outlet chamber. A vibrator containing an eccentrically movable mass, abuts and is engergizable directly through the top plate, without need for energizing hoses or conduits within the outlet chamber. The vibrator connects by a slim depending member to the bottom plate carrying the filter elements.
Other objects and purposes of the invention will be apparent to persons acquainted with apparatus of this general type upon reading the present specification and inspecting the accompanying drawings.